Japanese lawmakers have elected Naoto Kan as the country's new prime minister, two days after the surprise resignation of Yukio Hatoyama.

Mr Kan, the outgoing finance minister, promised economic reform and a focus on social welfare, as well as smooth ties with the US.

He becomes Japan's fifth prime minister in three years.

Mr Hatoyama resigned as prime minister on Wednesday in a dispute over a US military base in southern Japan.

He had promised to move the airbase off Okinawa Island, but failed to find an acceptable compromise to please locals and the US.

Mr Kan said that he would continue the programme of reform set out by his predecessor.

Mr Hatoyama led the Democratic Party of Japan (DPJ) to a historic election victory in September 2009, ousting the party which had led Japan for more than half a century.

"The hopes voters had for the Democratic Party are not just ending up as a mere dream. They will be realised," he said.

'Straight-talker'

Mr Kan was elected by DPJ lawmakers and then confirmed as prime minister by votes in both houses of parliament.

Analysis

By Roland BuerkBBC News, Tokyo

Naoto Kan has said his priority is to revive Japan's economy, growing slower than any other in Asia and certain to be overtaken as the world's second biggest by China soon.

He must try to mend ties with Japan's main security ally, the US, strained by the row over an American military base on the southern island of Okinawa which brought down Mr Hatoyama.

His toughest task may be to recapture the sense of hope felt when the Democratic Party of Japan won its landslide election victory last year, and ousted the conservatives who had governed for almost the entire post-war era.

The party promised clean, transparent politics, to put power in the hands of people rather than bureaucrats and to improve Japan's ties with its Asian neighbours. But it has squandered its support with broken promises and money scandals.

Mr Kan will not have long to impress. Elections to the less powerful upper house of the Diet, seen as a referendum on the government's performance, are due within weeks.

He defeated little-known Shinji Tarutoko, chairman of the lower house environmental committee, by a vote of 291-129 among DPJ members of parliament.

Mr Kan is expected to form a cabinet in the next few days, and to be sworn in by Emperor Akihito next week.

In a speech to DPJ members on Friday, Mr Kan said rebuilding the economy was his priority.

"I believe we can achieve a strong economy, strong finances and strong social welfare all at the same time," he said.

He said that the alliance with the US would remain the "cornerstone" of Japan's diplomacy.

But he made no pledges about the Okinawa base row that brought down his predecessor.

And he said that the party needed to unite ahead of upper house polls due in July.

"We will work together as one in the face of the tough political situation and the upcoming upper house elections and fight together unified," he said.

"Our first priority is to regain the trust of the people."

Mr Kan, 63, took over the finance ministry in January and has also been serving as deputy prime minister.

The BBC's Roland Buerk in Tokyo says he is seen as a straight-talker with a reputation for standing up to the powerful bureaucracy.

He has pushed for higher taxes and spending cuts to tackle Japan's national debt, the biggest in the industrial world.

He is one of the DPJ's most high-profile politicians because of his role in exposing a scandal involving HIV-tainted blood products in the 1990s.

Our correspondent says the new prime minister will have to move quickly to impress voters and to reinvigorate a centre-left government, which many believe has lost its way after just nine months.